“I knew truth was really important for the film so we could tell them if something wasn’t really a Scottish word and give them another one.”

Kelly – who is filming the third series of HBO gangster hit Boardwalk Empire – says that, while she borrowed key words from her mum, she couldn’t take anything else from her for the part – as she gets on too well with her.

Merida and her mum clash constantly and their arguments spark all the magical action.

But Kelly said: “I wasn’t rebellious. When I went for the part in Trainspotting, which was a risky part, my mum was very supportive.

“I was strong-minded but didn’t have what she has to rebel against.

“There were issues with my mum but all teenagers have that. Every time I said the word ‘mum’ as Merida, I remember saying that in the exact tone sometimes.”